Carbon blacks are widely used as reinforcing agents for elastomeric compositions. Carbon blacks contain residues or contaminants including soft coke, magnetic particles, and large agglomerates of carbon black that cannot be broken down. Carbon blacks having relatively high amounts of contaminants or relatively large contaminant particles tend to cause macro defects when used in extruded compositions, for example, an extruded elastomeric and/or polymeric composition such as a rubber sealant, a door seal, a car gasket, or other profile extrudates. There is a need to determine the amount of contaminants in a carbon black so that the suitability of the carbon black for use as a filler in an extruded composition can be accurately predicted.
A test method for determining the amount of residue in a carbon black sample is ASTM test method D-1514. Unfortunately, ASTM D-1514 does not accurately take into account the amount of soft coke in the sample as residue. Thus, ASTM D-1514 cannot be relied upon to accurately provide a prediction of macro defect formation in an extrudable composition containing carbon black. Results of the ASTM D-1514 test method have proven not to correlate with an extruded tape test wherein a thin test tape of a compounded material is extruded and visually inspected for macro defects. The number of macro defects is counted either visually or using an image analyzer. This method of counting defects above 200 .mu.m in diameter on the surface of an extruded tape has been shown to accurately predict product performance in extruded filled ethylene-propylene diene rubber (EPDM) compositions.
Accordingly, there is a need to develop a method of determining the amount of contaminants, including soft coke, in a carbon black sample. It is desirable to develop a carbon black residue test that correlates well with the extruded tape test and which can accurately predict product performance of extruded products containing carbon black.